Atea Pharmaceuticals Begins First Human Trial of AT-587 for Hepatitis E Virus

Atea Advances a New Oral Antiviral Candidate Into Clinical Testing

Atea Pharmaceuticals has started the first-in-human Phase 1 clinical trial of AT-587, an investigational oral antiviral being developed to treat hepatitis E virus (HEV) infection.

The company is taking an important step into clinical development after encouraging preclinical research showed that AT-587 has the potential to block HEV replication. If successful, the therapy could provide a much-needed treatment option for patients living with this viral liver disease, especially those with weakened immune systems who currently have very limited treatment choices.

Why Hepatitis E Still Needs Better Treatment

Hepatitis E is a viral infection that mainly affects the liver. In many healthy people, the infection clears on its own. However, the disease can become much more serious in people with weakened immune systems.

Patients who have received organ transplants, those taking immunosuppressive medicines, or people with certain blood cancers face a much higher risk of developing chronic hepatitis E. In these patients, the infection can continue for months or years and may eventually lead to cirrhosis, liver failure, and other severe complications.

Despite these risks, there are currently no approved antiviral treatments specifically developed for hepatitis E.

AT-587 Is Designed as an Oral Antiviral Therapy

AT-587 is a proprietary nucleotide analog developed by Atea Pharmaceuticals. It is designed as an oral antiviral medicine that works by interfering with the virus's ability to replicate inside the body.

Because the treatment is taken by mouth, it could offer a more convenient option compared to many injectable antiviral therapies used for other viral diseases.

The company believes the medicine may be particularly useful for transplant recipients and other immunocompromised patients who need an effective long-term treatment option.

Phase 1 Trial Has Officially Started

The newly launched Phase 1 study is the first time AT-587 will be tested in humans.

The trial is a randomized, double-blind, placebo-controlled, dose-escalation study involving healthy volunteers. Researchers will mainly evaluate:

• Safety
• Tolerability
• Pharmacokinetics (how the drug moves through the body)

The study has been divided into two separate parts.

Part A Will Test Single Doses

The first section of the trial will evaluate single ascending doses of AT-587 under fasting conditions.

One participant group will also receive the medicine after eating so researchers can understand whether food changes how the drug is absorbed.

This information will help determine the best way patients should eventually take the medicine.

Part B Will Evaluate Multiple Doses

The second part of the study will focus on repeated dosing.

Participants will receive AT-587 once daily or twice daily for seven consecutive days.

The doses selected for this stage will depend on the safety and pharmacokinetic data collected during Part A.

Researchers will continue reviewing new data throughout the trial before moving participants to higher dose levels.

Company Sees a Major Opportunity

According to Atea Pharmaceuticals Founder and CEO Jean-Pierre Sommadossi, hepatitis E continues to represent an important unmet medical need, particularly for immunocompromised patients who are at higher risk of chronic infection and serious liver disease.

He said the company believes AT-587 has the potential to become an important treatment option for transplant recipients and other vulnerable patients. He also noted that advancing AT-587 into human studies builds upon Atea's long experience in antiviral drug development while expanding the company's viral hepatitis research pipeline.

Earlier Research Produced Encouraging Results

Before entering clinical testing, AT-587 produced promising findings in several laboratory and animal studies.

Data presented at the EASL Congress 2026 showed that the investigational antiviral demonstrated strong activity against hepatitis E virus.

Researchers reported that AT-587 was approximately 30 to 150 times more potent in laboratory testing than ribavirin and sofosbuvir, two medicines currently used off-label or investigated for hepatitis E treatment.

The studies also found that:

• AT-587 effectively blocked HEV replication in laboratory models.
• No toxicity was observed during in vitro testing.
• The medicine remained active against drug-resistant HEV strains.
• Animal studies showed significantly lower viral RNA levels after treatment.

Researchers also observed antiviral activity against several other viruses, including flaviviruses, rubella virus, and chikungunya virus.

These findings suggest that AT-587 may have broader antiviral potential beyond hepatitis E.

Focus Is on Patients With Weak Immune Systems

Although hepatitis E affects millions of people every year worldwide, Atea's initial clinical focus will remain on patients who are most likely to develop chronic infection.

This includes:

• Organ transplant recipients
• Stem cell transplant patients
• Patients receiving immunosuppressive medicines
• Individuals with certain blood cancers

Each year, thousands of these patients across the United States and Europe remain at risk of developing chronic hepatitis E, yet no approved antiviral therapy is currently available.

Existing off-label treatments such as ribavirin often have limited effectiveness and may cause significant side effects.

Understanding Hepatitis E

Hepatitis E is caused by a single-stranded RNA virus that infects the liver.

Different virus genotypes are responsible for infections around the world. In developing countries, genotypes 1 and 2 are usually spread through contaminated water and often cause acute infections.

In the United States and Europe, genotype 3 is more common and is typically transmitted through food. While many healthy people recover without complications, chronic infection can develop in immunocompromised individuals and may eventually lead to irreversible liver damage.

Global estimates suggest that around 20 million acute hepatitis E infections occur every year, making it an important but often overlooked public health challenge.

Atea Continues Expanding Its Antiviral Pipeline

The launch of the Phase 1 trial adds another clinical program to Atea Pharmaceuticals' antiviral development portfolio.

The company focuses on discovering and developing oral antiviral medicines for serious viral infections with limited treatment options. By moving AT-587 into human testing, Atea aims to build a new therapeutic option for hepatitis E while strengthening its broader viral hepatitis research efforts.